DC Generator Objective Type Question Answer

38. Fig. 1 shows the external characteristic of …….. generator.

(i) over-compounded
(ii) series
(iii) flat-compounded
(iv) shunt

39. Referring to Fig. 1, the voltage drop at no. 2 is due to

(i) friction
(ii) armature reaction
(iii) field circuit
(iv) none of the above

40. Fig. 2, shows the external characteristics of a …… generator.

(i) shunt
(ii) flat-compounded
(iii) series
(iv) over-compounded

41. Fig. 3 shows the external characteristics of three types of generators having the same rating. Curve 2 represents for generator.

(i) shunt
(ii) separately-excited
(iii) compound
(iv) none of the above

42. Curve 3 in Fig. 3 represents the external characteristic of a generator.

(i) compound
(ii) separately-excited
(iii) shunt
(iv) none of the above

43. Curve 1 in Fig. 3 represents the external characteristic of a generator

(i) shunt
(ii) series
(iii) flat-compounded
(iv)none of the above

44. The curve B in Fig. 4 is the external characteristic of a generator.

(i) shunt
(ii) series
(iii) flat-compounded
(iv) under-compounded

45. The curve A in Fig. 4 represents the external characteristic of …… generator.

(i) shunt
(ii) flat-compounded
(iii) under-compounded
(iv) an over-compounded

46. The terminal voltage of a ……… generator vary widely with changes in load current.

(i) series
(ii) shunt flat-compounded
(iv)none of the above

47. The effect of armature reaction is to

(i) decrease the total flux
(ii) increase the total flux
(iii) make the air-gap flux uniform
(iv) none of the above

48. In a d.c. generator, armature reaction ……. pole tip.

(i) weakens the flux at the trailing
(ii) weakens the flux at the leading
(iii) strengthens the flux at the leading
(iv) none of the above

49. The armature of a d.c. machine having 10 poles is rotating at a speed of 10 revolutions per second. The number of hysteresis loops formed per second is

(i) 100
(ii) 10
(iii) 150
(iv) 50

50. The greatest percentage of heat loss in a d.c. machine is due to

(i) eddy current loss
(ii) hysteresis loss
(iii) copper loss
(iv) frictional loss

51. The size of a d.c. generator can be reduced by using ………

(i) lap winding
(ii) high-resistance winding material
(iii) iron commutator
(iv) magnetic material of high permeability

52. Hysteresis loss in a d.c machine is directly proportional to

(i) speed
(ii) (speed)²
(iii) (speed )^1.6
(iv) none of the above

53. The physical size of 100 kW, 2000 r.p.m. generator is ……… that of 10 kW, 200 r.p.m. generator.

(i) more than
(ii) less than
(iii) about the same as
(iv) none of the above

54. ……… together are called stray losses.

(i) copper and iron losses
(ii) iron and mechanical losses
(iii) field copper loss and iron loss
(iv) frictional loss and copper loss

55. The armature conductors of a 6-pole, lap-wound d.c. generator are divided into

(i) 2 parallel paths
(ii) 4 parallel paths
(iii) 3 parallel paths
(iv) 6 parallel paths

56. The efficiency of a d.c. generator is maximum when its variable loss is

(i) equal to constant loss
(ii) equal to half of constant loss
(iii) equal to double the constant loss
(iv) none of the above

57. In a cumulatively compounded generator, the shunt and series fields ……. each other.

(i) aid
(ii) oppose
(iii) sometime aid, sometime oppose
(iv) none of the above

58. Which of the following will not prevent a self-excited shunt generator from building upto its full voltage ?

(i) wrong direction of rotation
(ii) open field
(iii) no residual magnetism
(iv) speed too high

59. The curve showing the relation between the terminal voltage V and load current I_L of a d.c. generator is called its …….. characteristic.

(i) magnetic
(ii) external
(iii) internal
(iv) none of the above